1. Field of the Invention
This invention relates to the field of high voltage equipment enclosures, and in particular to an enclosure for a ballast assembly in a lighting fixture.
2. Description of Related Art
To prevent accidental shock or electrocution, safety standards have been established that require certain electrical assemblies to be enveloped by an enclosure that prevents access to the electrical assembly. A ballast assembly that is used for providing a high voltage or high current signal to a lamp is a common example of an assembly that is required to be enclosed in a tamper-proof, or tamper-resistant, enclosure.
A variety of means have been employed in conventional ballast assemblies to prevent tampering. A sheet-metal enclosure is typically provided that has a base unit and a cover unit. In some assemblies, the cover unit and base unit contain flanges, and the cover unit's flange is bent around the base unit flange on two or four sides. In order to gain access to the interior of the formed enclosure, one must un-bend the corner cover flanges; typically, this requires the use of a pair of pliers. In other assemblies, tabs are provided in the cover, and matching slots are provided in the base. After placing the cover on the base, with the tabs extending through the base, the tabs are bent or twisted to affix the cover to the base. To remove the cover, the tabs must be un-bent or un-twisted, again typically requiring a pair of pliers. In each of these bent-metal sealing techniques, it is difficult to return the enclosure to its original condition after un-bending the cover to gain access. In other assemblies, screws or nuts and bolts are used to affix the cover to the base; this has the advantage of ease of access to the interior for repairs, and a subsequent restoration of the enclosure to its original condition, using a screwdriver.
Although each of the prior mentioned fastening methods prevent an accidental access to the interior of the enclosure, they do not prevent a purposeful access to the interior by a potentially unqualified individual who has access to a pair of pliers or a screwdriver. More permanent sealing techniques can be employed, such as crimping the flanges of the cover and base together, using screws with heads that only allow tightening, and so on, but these approaches also make it difficult or impossible for a qualified person to gain access to the electrical assembly for repairs.
The above mentioned sealing techniques are somewhat costly to implement in a manufacturing environment, because they require a metal-bending step, or the insertion and tightening of screws or bolts. Snap-together techniques are preferred in a manufacturing environment, and a number of techniques are commonly used for snapping plastic parts together. Generally, if the plastic parts are well affixed to prevent tampering, an attempt to disassemble the parts causes damage to the parts. Alternatively, special tools may be designed to allow the qualified person to disassemble the parts without damaging the parts. On the other hand, if the plastic parts allow for an ease of disassembly without causing damage, and without requiring a special tool, an unqualified person can gain access to the interior of the enclosure. U.S. Pat. No. 5,691,878, "Snap-Lockable Housing for Fluorescent Lamp Ballasts", dated Nov. 25, 1997, illustrates a conventional plastic ballast enclosure. In this referenced patent, a base unit has plastic tabs that snap into recesses of a plastic cover. Although these tabs may facilitate assembly, an unauthorized person can easily open the enclosure by pushing on the tabs, using, for example, a small screwdriver or paperclip.